The objective of this project is to isolate and characterize mutants of Plasmodium falciparum to shed light on the parasites genetics, biochemistry and physiology which in turn will provide rational approaches for combating the parasite should the goal of an effective, inexpensive and easily administrable vaccine prove unattainable. Drug resistant mutants affecting the P. faciparum genes encoding dihydrofolate reductase-thymidylate synthase (DHFR-TS) in both the DHFR and TS domains (pyrimethamine resistance and CB3717 resistance); DNA polymerase alpha (aphidicolin resistance); and the largest subunits of either RNA polymerase I, II or Ill will be isolated and studied. The objects of isolating these mutants are to study the mechanisms of parasite drug resistance and to obtain temperature sensitive mutants for analyzing parasite growth and development as well as for the construction of parasites with multiple mutations effecting different defined essential genes that may be used as the basis for creating a live vaccine from an attenuated parasite. We will also examine the processes that may contribute to chromosome polymorphism formation. We will initially do this by examining agents that can stimulate DNA repair and recombination. We will study the prediction of larger chromosomal changes including gene amplifications and deletions as well as chromosome interactions in selected partially diploid mutants. We will also attempt to develop a DNA Transformation system in the parasite.